Hi,  I think that you will find that adding a flywheel to the Hofbauer
won't smooth it out very much.  The problem is that you aren't turning
the wheel very fast so the rotational inertia is small.  And a flywheel
adds quite a bit of weight to the organ.

But if you want to try it, you can get a much more finished flywheel
crank from Grizzly Tool Company.  They have a nicely finished 10-inch
flywheel for about $35 plus a few bucks for a handle.  Try

  http://www.grizzly.com/products/H3194 

You might want to check the adjustment on the arm (in your organ) that
goes from the offset in the crankshaft to the end of the bellows.  If
it's loose, the small amount of slop will exaggerate the uneven-ness in
the cranking.  Alternately, if you can add a small amount of friction,
it will make it feel more smooth.

Regards,

Craig Smith